Catalyst for purifying exhaust gas and method for purifying exhaust gas

Abstract

A catalyst for purifying an exhaust gas for simultaneously removing carbon monoxide, hydrocarbons and nitrogen oxides contained in the exhaust gas under an oxygen rich atmosphere, comprising a carrier composed of a porous material, and barium oxide, lanthanum oxide and platinum supported on the carrier, and a method for purifying an exhaust gas by bringing the exhaust gas under an oxygen rich atmosphere into contact with the above-mentioned catalyst.

We claim: 
     
       1. A method for purifying an oxygen rich exhaust gas simultaneously of, its contents of carbon monoxide, hydrocarbons and nitrogen oxides, comprising: bring the oxygen rich exhaust gas discharged from an engine into contact with a catalyst for purifying the exhaust gas consisting essentially of (i) at least one porous carrier material selected from the group consisting of alumina, zeolite, zirconia, silica and silica-alumina having applied thereto a combination of (ii) barium oxide and lanthanum oxide, at least a portion of each of the two oxide materials forming a composite barium-lanthanum oxide having the formula BaLa 2  O 4 , and (iii) platinum particles supported on the Ba,La oxide bearing carrier, the composite barium-lanthanum oxide being present in an amount sufficient to suppress the formation of LaAlO 3  which forms during operational use of the catalyst, which causes deterioration of the catalyst under the oxygen rich conditions of the exhaust gas treatment and to suppress the grain growth of platinum particles, which grain growth adversely affects the catalyst activity.   
     
     
       2. The method of claim 1, wherein, in the preparation of the exhaust gas purification catalyst, from 0.05 to 10.0 mol/l of a lanthanum compound is mixed with said alumina, zeolite or silica-alumina carrier in order to introduce lanthanum into the catalyst. 
     
     
       3. The method of claim 1, wherein, in the preparation of the exhaust gas purification catalyst, from 0.05 to 10.0 mol/l of a barium compound is mixed with said alumina, zeolite or silica-alumina carrier material in order to introduce barium into the catalyst. 
     
     
       4. The method of claim 1, wherein, in the preparation of the exhaust gas purification catalyst, from 0.05 to 10.0 mol/l of total combined lanthanum compound and barium compound is mixed with the alumina, zeolite or silica-alumina carrier material in order to introduce lanthanum and barium into the catalyst. 
     
     
       5. The method of claim 1, wherein, in the preparation of the exhaust gas purification catalyst, from 0.1 to 10.0 g/l of a platinum compound is mixed with the alumina, zeolite or silica-alumina carrier material in order to introduce Pt into the catalyst. 
     
     
       6. A method for purifying an oxygen rich exhaust gas simultaneously of its contents of carbon monoxide, hydrocarbons and nitrogen oxides, comprising: bringing the exhaust gas discharged from a lean burning engine in which the air-fuel mixture entering the engine ranges from the stoichiometric air-fuel ratio at idle, through the range of lean burning up to and including the overlean state which is an air/fuel ratio of about 23 which state occurs upon steady running and acceleration of the engine, into contact with a catalyst for purifying the exhaust gas consisting essentially of (i) at least one porous carrier material selected from the group consisting of alumina, zeolite, zirconia, silica and silica-alumina having applied thereto a combination of (ii) barium oxide and lanthanum oxide, at least a portion of each of the two oxide materials forming a composite barium-lanthanum oxide having the formula BaLa 2  O 4 , and (iii) platinum particles supported on the Ba,La oxide bearing carrier, the composite barium-lanthanum oxide being present in an amount sufficient to suppress the formation of LaAlO 3  which forms during operational use of the catalyst, which causes deterioration of the catalyst under the oxygen rich exhaust gas atmospheric conditions and to suppress the grain growth of platinum particles, which grain growth adversely affects catalyst activity, and whereby any NO x  produced upon combustion, which is not reduced to N 2  under the exhaust gas atmospheric conditions which vary consequently in relation to said range of the air-fuel mixture from the stoichiometric air-fuel ratio to the overlean state, is adsorbed by the composite oxide, which adsorbed NO x , whenever experiencing a reducing state of the exhaust gas over the operational regime of the engine, is reduced to N 2  over the Pt of the catalyst.